This application relates to a control for a refrigerant system wherein pulse width modulation technique is utilized to improve refrigerant system control and wherein a discharge bypass is operated in conjunction with the pulse width modulation to reduce compressor power consumption.
Refrigerant systems are utilized in many applications to condition a climate controlled environment. In particular, air conditioners and heat pumps are employed to cool and/or heat air entering the climate controlled environment. The cooling or heating load in the environment may vary with ambient conditions, occupancy level, and changes in sensible and latent load demands, and as the temperature and/or humidity set points are adjusted by an occupant of the environment.
Various features are known for providing adjustments in refrigerant system capacity. One approach which has been utilized in the prior art for reducing the capacity of a refrigerant system is the use of pulse width modulation technique to control a fast acting solenoid valve on a compressor suction line. By rapidly cycling this valve utilizing pulse width modulation techniques, additional and accurate capacity control is provided.
The goal of the pulse width modulation control is to efficiently compress the refrigerant at reduced mass flow rates. This is done when the thermal load demand on the refrigerant system is lower than would be provided with a compressor that is fully loaded.
However, this technique does not always achieve the goal of desired efficiency improvement, because even though the suction pressure is reduced substantially when the suction valve is closed (or almost closed), the discharge pressure still remains high causing a compressor power consumption to be higher than desired. Moreover, the compressed refrigerant on the discharge side can backflow into the compression chambers, further increasing compressor power consumption due to this backflow refrigerant re-compression. This problem is particularly acute in compressors that are not equipped with a dynamic discharge valve (as is often the case for compressors used in standard air conditioning applications). The absence of the dynamic discharge valve causes the compressed refrigerant at the discharge pressure to flow back into the compressor compression pockets, promoting increased power consumption. However, the problem also exists in compressors with a dynamic discharge valve, where the refrigerant still needs to be compressed to the discharge pressure. Refrigeration type compressors would normally be an example of compressors used with a dynamic discharge valve.